Marjah, Afghanistan (CNN) -- Foreign and Afghan forces encountered stiff resistance Saturday as their offensive in southern Afghanistan entered its second week, and a civilian was mistakenly shot dead.

"It is moving slowly but surely. The Marines are making some headway," said CNN correspondent Atia Abawi, who is embedded with U.S. Marines in and around Marjah in southern Afghanistan. "The Taliban are putting up quite a resistance."

She said the militants, who usually operate in squads of 10 to 14 fighters, don't have the weaponry and technology that the U.S. troops have, but they are able to put up a tough fight from fortified compounds and even civilian homes.

"The firefights have been going on all week long," Abawi said.

Operation Moshtarak, aimed at ousting the Taliban from their stronghold in Helmand province, is being conducted in and around the Marjah area by predominantly American and Afghan troops. British troops and their Afghan partners have been concentrating in the Nad Ali district. Troops are working to oust the Taliban and establish Afghan control.

Abawi said Marines have been creating a forward operating base "to prove to the people of Marjah as well as to the Taliban and insurgency in the area that they're here to stay" and hope to bring "normalcy" to the area.

NATO's International Security Assistance Force said on Friday the battle against the Taliban remains "difficult" in the northeast and west of Marjah, and insurgent activity is not limited to those areas.

British forces say Taliban resistance has increased in recent days, and that has slowed progress, despite strides.

On Friday, British officials said more than two-thirds of the Moshtarak clearance phase is completed. But British Maj. Gen. Gordon Messenger said with that effort, "resistance in that area has increased. We did expect the enemy to up the level of resistance, and that has happened.

"ISAF and Afghan forces are being directly targeted more now than they were before, but the enemy is still uncoordinated."

Messenger said providing extra security to key roads between Nad Ali and Lashkar Gah, Helmand's capital, are high priorities.

"Freedom of movement is vital so that locals can go about their business without fear of IEDs on the road and so we can bring key supplies into the area, and so the Afghan governors can get out to do their business," Messenger said.

Foreign and Afghan forces have taken pains to avoid civilian casualties in the operation. Civilian deaths and injuries during the Afghan war during airstrikes, raids and so-called "escalation of force" confrontations at checkpoints have undermined NATO efforts to get Afghans on their side.

But despite such efforts, such casualties have occurred in Moshtarak, with the latest coming on Friday, when coalition troops shot dead a man they mistook for a militant.

ISAF said the incident occurred in Nad Ali on Friday when an ISAF patrol thought he might have been carrying a bomb in a box.

"The patrol warned the individual by waving their hands, providing verbal warnings, and firing small pen flares into the air. The man dropped the box, turned and ran away from the patrol, and then for an unknown reason turned and ran toward the patrol, at which time they shot and killed him," ISAF said in a news release.

Later, troops discovered that there was no bomb material. Troops will meet with local leaders to discuss how to avoid such incidents, and a condolence payment will be offered to the victim's family.

"This is truly a regrettable incident, and we offer our condolences to the family," said Navy Capt. Jane Campbell, ISAF Joint Command spokeswoman.

Afghan President Hamid Karzai addressed the issue in parliament on Saturday, acknowledging efforts to improve but stressing that more has to be done.

"Regarding the civilian causalities in airstrikes and operations, the NATO and coalition forces have tried to conduct their operations carefully and responsibly to avoid civilian casualties," he said. "As a result civilian casualties have decreased. Our goal is to completely avoid the civilian casualties."